1. Field of the Invention
The present invention relates to an image formation apparatus for performing image processing.
2. Description of the Prior Art
In a conventional analog copying machine, in order to perform a copy operation, an intensity (or density) key or a diaphragm dial is adjusted in accordance with the intensity of an original so as to set a desired intensity (density) level. This operation requires a test copy operation, resulting in an uneconomical operation and poor operability. However, when recent developments in AE technologies in the field of copying machines, a method has been proposed in which the intensity of an image is measured with reflected light from the image or an electrostatic latent image on a photosensitive body is detected by an electrostatic sensor so as to discriminate the contrast, thereby forming images of optimal intensities. However, in practice, this method of detecting an intensity of an image does not allow clear discrimination between a line image portion and a solid image portion, and an optimal image may not be obtained. In a copying machine, in order to produce a copy image of an original image, the original is set on an original table or glass contact and covered with a cover so as not to allow ambient light to become incident on the optical system of the copying machine. If ambient light becomes incident on the optical system, the portion of the reproduced image corresponding to a light incident portion is reproduced black in color. In this case, an extra amount of toner is attached to this portion of the image, which is not preferable from the viewpoint of the characteristics of the photosensitive body. However, when the original is covered with the cover, the set condition of the original cannot be visually confirmed. For this reason, when the original is not placed at a suitable position on the original table or the original is of a size larger than a predetermined size, only poor image reproduction can be performed.
Originals include various documents such as thin sheets or book documents. In particular, a book has a considerable thickness. When an image of a certain page of such a book is to be copied, a shadow is formed at an edge of the book. This results in a black frame corresponding to an edge of a reproduced image, or a black stripe is formed at the center of the image, resulting in a poor image and in a poor operability.